Microwave Data Systems MDS 4310, Installation, Operation & Field Maintenance

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MDS 05-2415A01, Rev. A INSTALLATION 2-11
PIN 24: ETC—External Transmit Clock
This pin is used only on applications requiring a synchronous interface with an
external device controlling the timing of the transmitted bits. The most common
application of this pin is where the MDS 4310 is connected to an external high
speed modem. In this case, a cross-over (“null-modem”) cable is required that
connects Pin 17 (RC) from one modem to Pin 24 (ETC) of the other, and vice
versa. In most instances, timing is controlled by the internal clock inside the MDS
4310 (from Pin 15), and Pin 24 should be left open. The External Transmit Clock
signal is compatible only with RS-232 interfaces.
PIN 25: Out-of-Lock Alarm
A logic low (
≤
0.5 volts) on this pin indicates normal operation. A logic high
(
≥
4 volts) indicates a failure in the main phase lock loop or TCXO, or a trans-
mitter time-out condition. A logic high also causes the transmitter and receiver to
be shut down. This pin can be used as an alarm output, if the internal series
resistance of 1 k
Ω
is considered when designing an external interface circuit.
FRONT PANEL INDICATORS
The radio is supplied with a set of six light emitting diode indicators (LEDs) that provide
information on the status of key operating functions. The indicators can be disabled if the
jumper on the transceiver’s main board at J11, pins 2 & 2 is removed. With the pins bridged,
the display is enabled. There are two versions of the plastic label for the front panel of the
radio—one for radios without a modem installed (See Table 2-2), and one for radios with
internal modems (See Table 2-3).
Table 2-2. External Indicators
PWR TX CD
RTS TXD RXD
LED FUNCTION INDICATES
PWR Power Indicator Primary power is applied and is greater than 10
Vdc.
If this indicator is flashing, the VCO is out-of-lock.
All transmit and receive functions are disabled.
TX Transmit The transmitter is keyed and is on-the-air
CD Carrier Detect Receiver detects an on-channel signal and the
squelch is open.
RTS Request To Send The RTU is asserting a Request To Send signal.
TXD Transmit Data Reflects the current state of the Transmit Data
line from the Remote Terminal Unit (RTU).
LED OFF=0, LED ON=1
RXD Receive Data Reflects the current state of the Receive Data line
from the transceiver internal modem.
LED OFF=0, LED ON=1